Swelling of articular cartilage and other connective tissues: electromechanochemical forces.

We have measured the relationship between tissue swelling stress and consolidation for bovine articular cartilage and corneal stroma in uniaxial confined compression as a function of bath ionic strength. Our experimental protocol and results clearly demonstrate that two concentration-dependent material properties are necessary to describe the chemical dependence of tissue swelling stress in uniaxial compression over the range of deformations and concentrations explored. A general electromechanochemical model for the swelling stress of charged connective tissues is developed. The model focuses on the role of charged matrix macromolecules in determining the mechanical behavior of the tissue. A constitutive relation for the swelling stress in uniaxial confined compression is formulated and the concentration dependence of the material properties of articular cartilage and corneal stroma is determined. The associated free swelling behavior of cartilage and cornea specimens is computed from these results and is found to compare favorably with data from the literature.